HRP970388A2 - Mixtures of organosilan-polysulfanes and process for the preparation of rubber mixtures containing them - Google Patents

Abstract

A mixture (I) of organosilane polysulphides (II) of formula (RO)3Si(CH2)xS-Sz-S(CH2)xSi(OR)3 (1) is new. The mixture contains 20 wt.% or less (1) when z = 2-6 and less than 80 wt.% (1) when z = 0. In (1), R = 1-8C alkyl, preferably 1-3C alkyl; x = 1-8; and z = 0-6. Also claimed are (i) preparation of sulphur, sulphur donor and accelerator vulcanised rubber mixtures containing one or more natural or man-made rubber, silicate, fillers, optionally carbon black and other components, the rubber, fillers, carbon black, optionally plasticiser, anti-oxidants, activators and (I) being mixed at 160-200 degrees C for 3-15 minutes followed by the addition of vulcanisation agents at 60-120 degrees C and mixing for a further 2-10 minutes to yield sheet or strips; (ii) tyre tread compounds with a high silicic acid content containing 4-10 parts weight (pts. wt.) (I) to 100 pts. wt. filler.

Description

The invention relates to mixtures of organosilanepolysulfanes with a high content of disulfans and to a process for the production of rubber mixtures containing these compounds.

Savings in the consumption of motor fuels and reducing the emission of harmful substances are receiving a growing priority today, with increased awareness of the environment [1,2]. For the tire manufacturer, this means developing tires that feature very low rolling resistance, excellent wet skid resistance, and good wear resistance.

In many publications and patents, proposals have been made to reduce the tire's rolling resistance and thus the consumption of engine fuel. The reduction of the soot content in the mixture as well as the use of special soots (US patent 4,866,131, US patent 4,894,420) were mentioned. None of these proposed solutions, however, led to a satisfactory balance between the desired low rolling resistance and the equally important properties of the rubber, such as durability, wet sliding and wear resistance. Only the application of highly active fillers with silicic acid in combination with organosilane. Bis (triethoxysilylpropyl) tetrasulfane (TESPT) in the further replacement of carbon black with silicic acid in the rubber compound shows a path that enables the production of rubber with, compared to standard tires, extremely reduced rolling resistance while simultaneously maintaining or even improving both of the further above-mentioned tire properties [3, 4,5,6].

During the ACS-Meetings in 1986 in New York, S. Wolff [7] presented that by applying silicic acid in combination with TESPT, both in the running surface for passenger vehicles based on emulsion-styrene-butadiene rubber (E-SBR) and and for truck treads, based on natural rubber, it manages to clearly reduce the rolling resistance compared to the standard compound filled with carbon black, while still maintaining wet skid resistance.

Further optimization of this system with regard to all three properties was achieved by using special styrene-butadiene polymers, produced according to the dissolution and polymerization process (EP 0 447 066 A1), partly in a mixture with other polymers, especially with polybutadiene and additional application of new types of silicic acids (US patent 5,227,425) as well as specifically for this application designed polymer mixtures (EP 0 620 250 A1) with partially three to four different starting polymers [8,9].

In all publications and patents, it is described that in order to achieve a lower rolling resistance, while maintaining or improving wet sliding resistance and wear resistance, a large part, or the total content of the commonly used filler with carbon black, must be replaced with highly active silicic acid [7 ,9]. This replacement, however, only leads to the desired goal, if the organosilane Bis(triethoxysilipropyl) tetrasulfane (TESPT) is applied as a "Coupling Agent" between the silicic acid and the polymer.

It is now known [10, 11], that the picture of values, which can be achieved by using organosilane in rubber mixtures, rests on two reactions that take place independently of each other. In one case, it occurs during the production of the mixture, primarily in the first stage of mixing at high temperatures until the reaction between the silanol groups of silicic acid and the trialkoxysilyl groups of the silane with the separation of alcohol (hydrophobization or modification reaction). The complete reaction is of decisive importance for the subsequent value picture. It, like all chemical reactions, proceeds faster at high temperatures [12], so the creator of the rubber mixture, wishing to shorten mixing times, could use as high a mixing temperature as possible. He is hindered in this effort by the fact that there is another, so-called rubber-reactive group TESPT from one of the statistically average tetrasulfane groups with significant proportions of higher sulfane chains, (S5-S8) [11].

This rubber-reactive group leads, according to general understanding, to the construction of the so-called filler/rubber bond, which determines the picture of the technical value of the rubber of the finished article (eg vehicle tires). This reaction, which is desirable during vulcanization, is influenced by the thermolability of the tetrasulfane group and more sulfane units. However, it causes big problems, as practice shows, if it appears already during the production of the raw mixture, during which time usually only the reaction between the filler and the silane should take place.

If the sulfur is separated from the long-chain sulfane units, it will be incorporated into the polymer chain. This causes the so-called pre-crosslinking with the result that the sheet of the mixture is stiffened, which can lead to unworkability of the raw mixture. Pre-crosslinking is measurable by determining the viscosity of the mixture.

EP-A1-0732 362, which was not previously published, describes the use of organosilane disulfides in rubber compounds.

However, these compounds must be very pure, i.e. have a disulfide content of at least 80%.

The task of the invention is to prepare mixtures of organosilanepolysulfanes, which at elevated temperatures, as they can occur in the production of raw rubber mixtures, that means rubber mixtures that can be vulcanized, in which the sulfur and accelerator/accelerators necessary for vulcanization are still missing, do not lead to pre-networking.

The subject of the invention are polysulfane mixtures, which fulfill this task. These are mixtures of organosilanepolysulfanes according to the general formula

(RO)3Si(CH2)X S-SZ - S (CH2)X Si(OR)3 (I)

in which they mean:

R = Alkyl, straight chain or branched with 1-8 C-atoms, especially 1-3 C-atoms,

x = one integer from 1-8,

z = 0 to 6,

where the sum of the share of organosilanepolysulfanes, in which z = 0 and z = 1, is > 80% (wt.), with the restriction that the share of compounds, in which z = 0, remains below 80%, and the share of organosilanepolysulfanes, in which z means an integer from 2 to 6, in mixtures it does not exceed 20%.

The latter should also be expressed through a content of ≤ 20% (wt.) and forms a decisive characteristic.

Proportions of polysulfanes with z = 7 or 8 cannot generally be found in the mixtures according to the invention. In exceptional cases, these are contents < 1%, for example in the form of pollution, which have no effect on the application of the mixtures according to the invention.

The sum of the ingredients must of course always be 100%, taking into account compounds with z = 7;8 if necessary.

Particularly suitable are those in which the proportions of organopolysulfan assume the following values:

z = 0 approx. 58 to < 80 %

z = 1 > 0 to ca. 32%, where the sum of these two compounds is > 80%, i

z = 2 to 6 < 20 %, especially < ca. 11%.

The compounds according to the invention are used in the production of vulcanizable rubber compounds, especially for tires. The polymers used there are natural and synthetic elastomers, stretchable like oil or not, as a single polymer or in a mixture with other rubbers, such as natural rubbers, butadiene rubbers, isoprene rubbers, butadiene-styrene rubbers, but especially SBR, produced according to the process of polymerization in solution or the process of emulsion polymerization.

The term mixture should be understood in such a way that, on the one hand, mixtures can be produced from pure polysulfanes according to formula (I) with x = 0 and other polysulfanes, in which x = 0, but which satisfies requirement 1.

On the other hand, it is still possible to obtain the mixtures according to the invention using a suitable production process directly or by mixing other polysulfanes.

Mixtures according to the invention are used above all in mixtures for driving surfaces with a high content of silicic acid, such as e.g. described in EP-A1-0447 066 and EP-A-0620 250.

With the application of mixtures according to the invention, the produced rubber mixtures are usually cross-linked with sulfur and/or sulfur donors and accelerators (vulcanization aid), whereby the amount of sulfur is usually between 0.1 and 4 phr.

They contain, in addition to polymers and additives common in practice as activators, protective substances against aging, auxiliary means for finishing, if necessary carbon black and also natural, light fillers, but in any case highly active fillers with silicic acid in amounts from 10 to 200 parts, especially 25 to 80 parts, compared to 100 parts of polymer. These fillers are characterized by having BET surfaces of 1 to 700 m2/g, especially 100 to 250 m2/g, and in addition a DBP number of 150 to 300 ml/100 g. As the forms offered, they are suitable at the same time powder, but also non-powder forms, such as granules and microgranules.

The amount of mixtures according to the invention amounts to between 0.5 and 30 parts, compared to 100 parts of the filler. In particularly suitable applications, such as road mixtures, surfaces with high proportions of silicic acid, in which, as a rule, silicic acid is used with 100 to 250 m2/g, quantities between 4 and 10 parts of the mixture according to the invention are applied, in relation to 100 pieces of filler.

The mixtures according to the invention can be brought to the mixture in situ or, in the better form offered, specially mixed with carbon black. A pre-modification of silicic acid applied as a filler is also possible, as described for example in DE 196 09619.7.

Special attention should be paid to the process for the production of mixtures filled to a large extent with silicic acid in combination with organosilanes. A suitable procedure is described in the application EP 0 447 066 A1, however, for the purpose of applying TESPT there, it is necessary not to allow the temperature during the production of the mixture to rise above 160 °C, so as not to cause the pre-crosslinking described above. When using the compounds according to the invention, temperatures of 160 to 200 °C, especially 175 to 190 °C, are still possible without the appearance of this annoying effect.

The creator of the mixture can therefore choose higher temperatures and thereby accelerate the reaction between silicic acid and silane, which means reducing the mixing time and/or the number of mixing stages. He thus has the greatest freedom to choose his mixing conditions.

The compounds according to the invention can be used in almost all rubber articles. They are particularly suitable for the application of compounds with a high content of silicic acid (content > 40 parts of SiO2), in relation to 100 parts of rubber, especially in compounds for tire treads, in which, as a rule, large amounts of silane must be applied to achieve the required image values.

The described rubber mixtures, as well as the production process, are the subject of the invention.

The process for the production of rubber mixtures vulcanized with sulfur and/or sulfur donors and accelerators, containing one or more natural or artificial rubbers, light oxide (silicate) fillers, as well as, if necessary, carbon black and other common ingredients, is characterized by the fact that the component (e) of the rubber, the mixture according to requirements 1, 2 or 3, the silicate filler and, if necessary, the available carbon black, as well as in the given case the softener, antiaging agent and activators, are kneaded in a kneading device, in the given case in a Banbury piston kneader at a temperature of 160 to 200 °C, especially 175 to 190 °C, 3 to 15 minutes in one stage or multiple stages, then at 80 to 120 °C, primarily at 80 to 110 °C, to which a vulcanizing agent is added, or in a Banbury reciprocating kneader or on a mixing roller, it is mixed in the specified temperature range for a further 2 to 10 minutes, and the finished rubber mixture is then taken out as a rubber sheet or in the form of strips.

This invention therefore also refers to the use of organosilanepolysulfane mixtures, the distribution of which, the sulfane chains, is chosen in such a way that even at temperatures of 160 to 200 °C, especially 175 to 190 °C, pre-crosslinking of the raw mixture is not noticeable.

In practice, this pre-crosslinking can be assessed on the basis of the properties of the sheet of raw mixture, which becomes rougher and more crumbly during the subsequent pre-crosslinking and often cannot be processed on the roller anymore. In the laboratory, this pre-crosslinking can be proven by measuring the viscosity of the mixture as well as by determining the minimum value of the torsional moment of the raw mixture during the rheometric test. An increase in viscosity of more than 5, especially more than 10 Mooney units according to the formulation mixed at a lower temperature (= safe processing behavior) can be used as a guideline value as a pre-crosslinking measure.

Literature:

[1] Auto 91/92, Verband der Automobilindustrie e.V., Frankfurt.

[2] ADAC-Motorwelt 11791, 50 (1991). [3] EP 0 501 227, US 5,227,425

[4] G. Agostini, J. Berg, Th. Materne: New Compound Technology. October 1994, Akron, Ohio/USA.

[5] S. Wolff, U, Goerl, M.J. Wang, W. Wolff: Silica based on Tread Compounds - Background and Performance, Lecture held at TIRE TECH 93, Oct. 1993, Basel/Switzerland.

[6] Ph. Cochet, L.B. Barriguand: Precipitated Silica in Tire Tread, Lecture delivered at the ACS Meetings of the Rubber Division, Oct. 1995, Cleveland, Ohio/USA.

[7] S. Wolff: The Influence of Fillers on Rolling Resistance, presented at the 129th Meeting of the Rubber Division of the American Chemical Society, April 8-11, 1986, New York.

[8] G.W. Marwede, U.G. Eisele, A.J.M. Sumner: Lecture held at the ACS Meetings of the Rubber Division, Oct. 1995, Cleveland, Ohio/USA.

[9] U. LeMaitre: The Tire Rolling Resistance, AFCEP/DKG-Meeting. 1993, Mulhouse/France.

[10] S. Wolff: The Role of Rubber-to-Silica Bonds in Reinforcement, presented at the First Franco-German Rubber Symposium, Nov. 14-16, 1985, Obernai/France.

[11] S. Wolff: Silanes in Tire Compounding after Ten Years - Review - Third Annual Meeting and Conference on Tire Science and Technology, The Tire Society, March 28-29, 1984, Akron, Ohio/USA.

[12] U. Goerl, A. Hunsche: Advanced investigations into the Silica/Silane Reaction System, Lecture at ACS Meetings, Rubber Division, Oct. 1996, Louisville, Kentucky/USA.

[13] Houben-Weyl: Herstellung von Disulfiden, Methoden der organischen Chemie 1955. (Production of Disulfide, Methods of Organic Chemistry, 1955).

In the examples, the test norms were applied:

[image]

In the application examples, the following chemicals were used:

Si 69 Bis (triethoxysilylpropyl) tetrasulfane (Degussa AG)

Buna VSL 5025 1 HM Styrene-butadiene-rubber, produced according to the process of dissolution and polymerization (Bayer AG).

Buna CB 11S Polybutadiene rubber (Bayer AG).

Naphtolene ZD Aromatic softener (Chemetal).

Vulkanox 4020 Phenylenediamine-based (Bayer AG) (6PPD) anti-aging discolouration protectant.

Protector G 35 Ozonized protective wax (Fuller).

Vulkacite D Diphenylguanidine (Bayer AG)

Vulkacite CZ Benzothiazyl-2-cyclohexylsulfenamide (Bayer AG)

Ultrasil VN 3 GR Precipitated silicic acid with a BET surface area of 175 m2/g (Degussa AG).

Si 266 Bis(triethoxysilylpropyl)disulfane

Si 266 mode In example 3: distribution of sulfane chains: 57.7% S2; 31.4% S3; 8.3% S4; 2.3% S5, 0.2% S6.

Example 1: Determination of the distribution of sulfane chains of different mixtures of organosilanepolysulfanes

Determination by the HPCL method for the following compositions:

[image]

Example 2: Determination of pre-crosslinking based on the rheometric curve at 180 °C

The overall mixtures from example 1 were introduced into the rubber mixture corresponding to example 3 at ca. 140 °C with the application of the mixing recipe for stages 1 and 2, that means without a pre-crosslinking system.

The minimum torsion value of these raw mixtures was then determined in a rheometer at 180 °C. An increase in the torsion value should be seen as an indication of pre-vulcanization behavior (see Figure 1).

Example 3: Comparison of data, raw mixture and rheometer data between Si 69 and disulfan mixture in passenger vehicle tread compound

The influence of the extraction temperature

[image]

(Si 266 mode: 57.7% S2, 31.4% S3, 8.3% S4, 2.3% S5, 0.2% S6).

Mixing regulation:

Degree 1

Blade rotation speed: 70 rpm

Flow: 80 °C

[image]

Degree 2

Blade rotation speed: 60 rpm

Flow: 80 °C

[image]

Degree 3

Blade rotation speed: 30 rpm

Flow: 50 °C

[image]

Mixing regulation:

Degree 1

Blade rotation speed: 95 rpm

Flow: 80 °C

[image]

Degree 2

Blade rotation speed: 60 rpm

Flow: 80 °C

[image]

Degree 3

Blade rotation speed: 30 rpm

Flow: 50 °C

[image]

Mixing regulation:

Degree 1

Blade rotation speed: 115 rpm

Flow: 95 °C

[image]

Degree 2

Blade rotation speed: 60 rpm

Flow: 80 °C

[image]

Degree 3

Blade rotation speed: 30 rpm

Flow: 50 °C

[image]

Data for vulcanizate: 165 °C / t95%

[image]

Based on the high extrusion temperature of 180 °C possible, with Si 266 mod, without the risk of pre-vulcanization, the data obtained for the vulcanizate can be compared with those of Si 69 at the extrusion temperature of 140 °C.

At the same time, the Si 266 mode is characterized by particularly good tan 8 values at 0 °C, which can be manifested in better properties of the tires' resistance to sliding in the wet.

[image]

Rheometer data: 165 °C

[image]

The Si 266 mode shows significantly better pre-vulcanization behavior at all mixing temperatures.

[image]

The Si 266 mode shows a distinctly more favorable vulcanization time compared to Si 69.

Data for raw mixture

[image]

Si 266 mode does not show pre-vulcanization behavior even at high mixing temperatures and is therefore extremely favorable in processing behavior.

Injection speed

[image]

The Si 266 mod has distinct advantages in injection speed.

Claims (8)

1. A mixture of organosilanepolysulfanes according to the general formula, characterized by the fact that (RO)3Si(CH2)X S-SZ - S (CH2)X Si(OR)3 (I) in which they mean R = Alkyl, straight chain or branched with 1-8 C-atoms, especially 1-3 C-atoms, x = one integer from 1-8, z = 0 to 8, where the proportion of polysulfanes, where z is an integer from 2 to 6, does not exceed a proportion of 20 wt. % in the mixture, and the proportion of polysulfane with z = 0 does not reach the value of 80 wt. %. 2. Mixtures according to claim 1, characterized by the fact that the sum of the proportion of organosilanepolysulfanes, in which z = 0 and z = 1, is > 80% (wt.), with the limitation that the proportion of the compound, in which z = 0, remains below 80 %, and the share of organopolysulfanes, in which z is an integer from 2 to 6, in the mixtures does not exceed 20%. 3. Mixtures according to claim 2, characterized by the fact that the proportions of organosilanepolysulfane in the mixtures assume the following values: z = 0 approx. 58 to < 80 % z = 1 > 0 to ca. 32%, where the sum of these compounds is > 80%, z = 2 to 6 and < 20 %. 4. Process for the production of rubber mixtures vulcanized with sulfur, and/or sulfur donors and accelerators, which contain one or more natural or artificial rubbers, light oxide (silicate) fillers, as well as, if necessary, carbon black and other common ingredients, characterized by kneading the rubber component (components), mixtures according to requirements 1 or 3, silicate filler and, if necessary, available carbon black, as well as, in the given case, a softener, an anti-aging agent and activators for 3 to 15 minutes at a temperature of 160 - 200 °C in one stage or in several stages in a kneading device, in the given case a Banbury reciprocating kneader, then at 60 to 120 °C a vulcanization aid is added, either in a Banbury reciprocating kneader or on a mixing roller, in the specified temperature range, it is mixed for a further 2 up to 10 minutes and then pulls out the finished rubber mixture as a rubber sheet or in the form of strips. 5. The method according to claim 4, characterized by the fact that natural fillers (clays, silicic chalks) and/or precipitated silicic acid or silicates are used as bright oxide fillers in the amount of 10 to 200 parts, preferably 25 to 80 parts, in relation to 100 parts of polymer. 6. Process according to claims 4 and 5, characterized by the fact that fillers with a BET surface (ISO 5794/1D) of 1 to 700 m2/g are used, whereby the precipitated silicic acids and silicates also have a DBP number (ASTM D 2414 ) from 150 to 300 ml/100 g. 7. The method according to claims 4 to 6, characterized by the fact that an oxide filler mixed with the organosilanepolysulfane mixtures described in claim 1 and/or pre-processed is applied, whereby the applied amount of the mixture according to claim 1 per 100 parts of the filler is 0.5 to 30 parts . 8. Tread compounds for tires with a high silicic acid content, characterized in that they contain 4 to 10 parts of compounds according to claims 1, 2 or 3, in relation to 100 parts of filler.